Answer:
No. A marching french horn, also called a mellophone, has a shape more like a trumpet with a large bell facing forward. A "regular" french horn has the bell facing backwards. You use your left hand to play the french horn and your right hand to play the mellophone.
Fingering also changes to that identical to a trumpet, or a B-flat Horn (the E's and D's are fingered differently). Some mellophones are made to be used with a trumpet (cornet) mouthpiece, but there are adapters you can use to use your horn mouthpiece. Other mellophone are made to be used only with a horn mouthpiece.